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Zhang W, Khosropanah P, Gao JR, Kollberg EL, Yngvesson KS, Bansal T, et al. Quantum noise in a terahertz hot electron bolometer mixer. Appl Phys Lett. 2010;96(11):111113–(1.
Abstract: We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model for HEB mixers, we confirm the effect of QN. The QN is found to be responsible for about half of the receiver noise at the highest frequency in our measurements. The beta-factor (the quantum efficiency of the HEB) obtained experimentally agrees reasonably well with the calculated value.
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Huebers H-W, Pavlov S, Semenov A, Köhler R, Mahler L, Tredicucci A, et al. Terahertz quantum cascade laser as local oscillator in a heterodyne receiver. Optics Express. 2005;13(15):5890–6.
Abstract: Terahertz quantum cascade lasers have been investigated with respect to their performance as a local oscillator in a heterodyne receiver. The beam profile has been measured and transformed in to a close to Gaussian profile resulting in a good matching between the field patterns of the quantum cascade laser and the antenna of a superconducting hot electron bolometric mixer. Noise temperature measurements with the hot electron bolometer and a 2.5 THz quantum cascade laser yielded the same result as with a gas laser as local oscillator.
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Rabanus D, Graf UU, Philipp M, Ricken O, Stutzki J, Vowinkel B, et al. Phase locking of a 1.5 terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver. Optics Express. 2009;17(3):1159–68.
Abstract: We demonstrate for the first time the closure of an electronic phase lock loop for a continuous–wave quantum cascade laser (QCL) at 1.5 THz. The QCL is operated in a closed cycle cryo cooler. We achieved a frequency stability of better than 100 Hz, limited by the resolution bandwidth of the spectrum analyser. The PLL electronics make use of the intermediate frequency (IF) obtained from a hot electron bolometer (HEB) which is downconverted to a PLL IF of 125 MHz. The coarse selection of the longitudinal mode and the fine tuning is achieved via the bias voltage of the QCL. Within a QCL cavity mode, the free-running QCL shows frequency fluctuations of about 5 MHz, which the PLL circuit is able to control via the Stark–shift of the QCL gain material. Temperature dependent tuning is shown to be nonlinear, and of the order of -16 MHz/K. Additionally we have used the QCL as local oscillator (LO) to pump an HEB and perform, again for the first time at 1.5 THz, a heterodyne experiment, and obtain a receiver noise temperature of 1741 K.
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Ryabchun S, Tong C-YE, Paine S, Lobanov Y, Blundell R, Goltsman G. Temperature resolution of an HEB receiver at 810 GHz. IEEE Trans Appl Supercond. 2009;19(3):293–6.
Abstract: We present the results of direct measurements of the temperature resolution of an HEB receiver operating at 810 GHz, in both continuum and spectroscopic modes. In the continuum mode, the input of the receiver was switched between black bodies with different physical temperatures. With a system noise temperature of around 1100 K, the receiver was able to resolve loads which differed in temperature by about 1 K over an integration time of 5 seconds. This resolution is significantly worse than the value of 0.07 K given by the radiometer equation. In the spectroscopic mode, a gas cell filled with carbonyl sulphide (OCS) gas was used and the emission line at 813.3537060 GHz was measured using the receiver in conjunction with a digital spectrometer. From the observed spectra, we determined that the measurement uncertainty of the equivalent emission temperature was 2.8 K for an integration time of 0.25 seconds and a spectral resolution of 12 MHz, compared to a 1.4 K temperature resolution given by the radiometer equation. This relative improvement is due to the fact that at short integration times the contribution from 1/f noise and drift are less dominant. In both modes, the temperature resolution was improved by about 40% with the use of a feedback loop which adjusted the level of an injected microwave radiation to maintain a constant operating current of the HEB mixer. This stabilization scheme has proved to be very effective to keep the temperature resolution of the HEB receiver to close to the theoretical value given by the radiometer equation.
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Tretyakov I, Ryabchun S, Finkel M, Maslennikova A, Kaurova N, Lobastova A, et al. Low noise and wide bandwidth of NbN hot-electron bolometer mixers. Appl Phys Lett. 2011;98:033507 (1 to 3).
Abstract: We report a record double sideband noise temperature of 600 K (5hν/kB) offered by a NbN hot-electron bolometer receiver at 2.5 THz. Allowing for standing wave effects, this value was found to be constant in the intermediate frequency range 1–7 GHz, which indicates that the mixer has an unprecedentedly large noise bandwidth in excess of 7 GHz. The insight into this is provided by gain bandwidth measurements performed at the superconducting transition. They show that the dependence of the bandwidth on the mixer length follows the model for an HEB mixer with diffusion and phonon cooling of the hot electrons.
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Масленникова АВ, Рябчун СА, Финкель МИ, Каурова НС, Исупова АА, Воронов БМ, et al. Широкополосные смесители на горячих электронах на основе NbN наноструктур. Труды МФТИ. 2011;3(2):31–4.
Abstract: Мы приводим данные исследования полосы преобразования смесителей на горячих электронах (hot-electron bolometer, НЕВ), изготовленных на основе тонких пленок NbN. Зависимость полосы преобразования от длины смесительного элемента находится в прекрасном согласии с результатами теоретической модели HEB-смесителя, в котором энергетическая релаксация электронов одновременно происходит по двум каналам: фононному и диффузионному.
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de Lange G, Krieg J-M, Honingh N, Karpov A, Cherednichenko S. Performance of the HIFI flight mixers. In: Proc. 19th Int. Symp. Space Terahertz Technol.; 2008. p. 98–105.
Abstract: We summarize the technology and final results of the superconducting heterodyne SIS and HEB mixers that are developed for the HIFI instrument. Within HIFI 7 frequency bands cover the frequency range from 480 GHz to 1910 GHz. We describe the different device technologies and optical coupling schemes that are used to cover the frequency bands. The efforts of the different mixer teams that participate in HIFI have contributed to an instrument that will have unprecedented sensitivity and frequency coverage.
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Tret’yakov IV, Ryabchun SA, Kaurova NS, Larionov PA, Lobastova AA, Voronov BM, et al. Optimum absorbed heterodyne power for superconducting NbN hot-electron bolometer mixer. Tech Phys Lett. 2010;36(12):1103–5.
Abstract: Absorbed heterodyne power has been measured in a low-noise broadband hot-electron bolometer (HEB) mixer for the terahertz range, operating on the effect of electron heating in the resistive state of an ultrathin superconducting NbN film. It is established that the optimum absorbed heterodyne power for the HEB mixer operating at 2.5 THz is about 100 nW.
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Korneev A, Finkel M, Maslennikov S, Korneeva Y, Florya I, Tarkhov M, et al. Superconducting NbN terahertz detectors and infrared photon counters. Вестник НГУ Серия: физ. 2010;5(4):68–72.
Abstract: We present our recent achievements in the development of sensitive and ultrafast thin-film superconducting sensors: hot-electron bolometers (HEB), HEB-mixers for terahertz range and infrared single-photon counters. These sensors have already demonstrated a performance that makes them devices-of-choice for many terahertz and optical applications. Keywords: Hot electron bolometer mixers, infrared single-photon detectors, superconducting device fabrication, superconducting NbN films.
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Tretyakov I, Ryabchun S, Finkel M, Maslennikov S, Maslennikova A, Kaurova N, et al. Ultrawide noise bandwidth of NbN hot-electron bolometer mixers with in situ gold contacts. IEEE Trans. Appl. Supercond.. 2011;21(3):620–3.
Abstract: We report a noise bandwidth of 7 GHz in the new generation of NbN hot-electron bolometer (HEB) mixers that are being developed for the space observatory Millimetron. The HEB receiver driven by a 2.5-THz local oscillator offered a noise temperature of 600 K in a 50-MHz final detection bandwidth. As the filter center frequency was swept this value remained nearly constant up to the cutoff frequency of the cryogenic amplifier at 7 GHz. We believe that such a low value of the noise temperature is due to reduced radio frequency (RF) loss at the interface between the superconducting film and the gold contacts. We have also performed gain bandwidth measurements at the superconducting transition on HEB mixers with various lengths and found them to be in excellent agreement with the results of the analytical and numerical models developed for the HEB mixer with both diffusion and phonon cooling of hot electrons.
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